1. Field of the Invention
The present general inventive concept relates to an inkjet printhead having a hydrophobic layer, and more particularly, to a method of forming a hydrophobic coating layer on a surface of a nozzle plate of an inkjet printhead.
2. Description of the Related Art
An inkjet printhead is a device that ejects fine ink droplets onto a desired position of a recording medium to print an image of a predetermined color. The inkjet printhead may be roughly classified into two types of printheads, depending on an ink ejecting method employed: thermally-driven inkjet printheads and piezoelectric inkjet printheads. A thermally-driven inkjet printhead generates a bubble in ink using a heat source and ejects the ink using an expansion force of the bubble. A piezoelectric inkjet printhead deforms a piezoelectric element and ejects ink using a pressure applied to the ink due to the deformation of the piezoelectric element.
FIG. 1 is a sectional view illustrating a construction of a conventional piezoelectric inkjet printhead.
Referring to FIG. 1, a channel plate 10 includes a manifold 13, a plurality of restrictors 12, and a plurality of pressure chambers 11. A nozzle plate 20 includes a plurality of nozzles 22 corresponding to the pressure chambers 11. Also, a piezoelectric actuator 40 is provided on an upper portion of the channel plate 10. The manifold 13 is a passage supplying ink flowing from an ink storage (not illustrated) to each of the pressure chambers 11, and each of the restrictors 12 is a passage through which the ink flows from the manifold 13 into each of the pressure chambers 11. The plurality of pressure chambers 11, which are filled with ink to be ejected, are arranged on one side or both sides of the manifold 13. Each pressure chamber 11 changes its volume as the piezoelectric actuator 40 is driven, thereby creating a pressure change required for an ejection of ink or for an in-flow of ink. A portion that constitutes an upper wall of each of the pressure chambers 11 contained in the channel plate 10 serves as a vibration plate 14 that is deformable by a driving of the piezoelectric actuator 40.
The piezoelectric actuator 40 includes a lower electrode 41, a piezoelectric layer 42, and an upper electrode 43 sequentially stacked on the channel plate 10. A silicon oxide layer 31 is formed as an insulation layer between the lower electrode 41 and the channel plate 10. The lower electrode 41 is formed on an entire surface of the silicon layer 31 to serve as a common electrode. The piezoelectric layer 42 is formed on the lower electrode 41 such that the piezoelectric layer 42 is positioned on the plurality of pressure chambers 16. The upper electrode 43 is formed on the piezoelectric layer 42 to serve as a drive electrode, applying a voltage to the piezoelectric layer 42.
In the inkjet printhead having the above construction, water-repellent processing of a surface of the nozzle plate 20 has a direct influence on an ink ejection performance thereof, such as a directionality and an ejection speed of an ink droplet ejected through each of the nozzles 22. To improve an ink ejection performance, the surface of the nozzle plate 20 outside of the nozzles 22 should have a water-repellent characteristic, i.e., should be hydrophobic, and an inner wall of each of the nozzles 22 should be hydrophilic. In detail, when the surface of the nozzle plate 20 outside of the nozzles 22 is hydrophobic, ink wetting on the surface of the nozzle plate 20 is prevented, so that the directionality of ejected ink may be improved. Also, when the inner wall of each of the nozzles 22 is hydrophilic, a contact angle with respect to an ink droplet decreases and thus capillary force increases, so that a refill time of ink is shortened and an ejection frequency may be increased. Also, since each of the nozzles 22 is filled with ink up to an exit thereof, a uniformity of ink ejection may be improved.
A method of forming a hydrophobic coating layer over the entire nozzle plate 20 having the nozzles 22 therein using an electron beam evaporation method has been conventionally-used. According to this conventional method, the hydrophobic coating layer is formed on the inner wall of each of the nozzles 22, as well as the surface of the nozzle plate 20 outside of the nozzles 22. The hydrophobic coating layer formed on the inner wall of each of the nozzles 22 reduces refill characteristics of ink and ejection uniformity.
To solve these problems, conventional methods of forming a hydrophobic coating layer only on the surface of the nozzle plate 20 are under development.
FIG. 2 is a view illustrating a conventional inkjet printhead on which a sulphur compound layer is formed as a hydrophobic coating layer on a surface of a nozzle plate 51 thereof.
Referring to FIG. 2, after a metal layer 52 is formed on the surface of the nozzle plate 51 including a plurality of nozzles 55, each nozzle 55 being formed to pass through the nozzle plate 51, a sulphur compound is coated on the surface of the metal layer 52 to form a sulphur compound layer 53. The sulphur compound is selectively coated on the surface of the metal layer 52. However, according to this method, there is a high probability that the metal layer 52 is deposited on an inner wall of each of the nozzles 55 as well as the surface of the nozzle plate 51. Also, when a number of the nozzles 55 is large, the metal layer 52 may be non-uniformly deposited on different portions of each of the nozzles 55. In this case, the sulphur compound layer 53 may be formed on the inner wall of each of the nozzles 55 or may be non-uniformly formed. When the sulphur compound layer 53, which is a hydrophobic coating layer, is not properly formed, areas around each of the nozzles 55 are easily contaminated by ink and an ejection speed of an ink droplet is reduced or an ejection direction of an ink droplet becomes non-uniform, so that an ejection performance is impaired.
FIG. 3 is a view illustrating a conventional inkjet printhead on which a water-repellent layer including a fluorine resin is formed on a surface of a nozzle plate 70 thereof.
Referring to FIG. 3, a water-repellent layer 90 is formed on the surface of the nozzle plate 70 having nozzles 72. This water-repellent layer 90 includes a fluorine resin particle 94 and a hard body 98 contained in a nickel base 96. A fluorine resin layer 92 is formed on the surface of the water-repellent layer. However, since nickel is reactive with a portion of ink, nickel is undesirable for commercial use.
Japanese Patent Laid-Open Publication No. hei 7-314693 discloses a method of forming a water-repellent layer on a surface of a nozzle plate by blowing a gas through nozzles of the nozzle plate to prevent the water-repellent layer from being formed on an inner surface of each of the nozzles. However, this method requires a complicated apparatus and a difficult process, and thus it is difficult and expensive to use this method.